Hot air language - Home Energy Pros2016-12-10T05:21:25Zhttp://homeenergypros.lbl.gov/forum/topics/hot-air-language?xg_source=activity&id=6069565%3ATopic%3A138736&feed=yes&xn_auth=noBud
I think I have come up wi…tag:homeenergypros.lbl.gov,2013-10-25:6069565:Comment:1399022013-10-25T14:59:05.770ZEd Minchhttp://homeenergypros.lbl.gov/profile/EdMinch773
<p>Bud</p>
<p>I think I have come up with a way might make almost everyone happy:</p>
<p>Hot air rises while denser cold air falls, but since gravity is the force that is causing it, it is the cold air that starts the cycle.</p>
<p>Ed MInch</p>
<p>Bud</p>
<p>I think I have come up with a way might make almost everyone happy:</p>
<p>Hot air rises while denser cold air falls, but since gravity is the force that is causing it, it is the cold air that starts the cycle.</p>
<p>Ed MInch</p> Here is one of the useful det…tag:homeenergypros.lbl.gov,2013-10-16:6069565:Comment:1393402013-10-16T15:02:04.573ZBud Pollhttp://homeenergypros.lbl.gov/profile/EverettPoll
<p>Here is one of the useful details that I have uncovered from my work on stack effect (SE). To estimate the total SE available in a home at a given delta "t" simply multiply that temperature difference by the height of the house and by 0.007.</p>
<p>SE (pa) = .007 x ▲t (F) x ▲h (ft)</p>
<p>This gives you the total SE which gets divided in some proportion between high and low with that ever elusive neutral pressure plane (NPP) somewhere in between. </p>
<p>Now, knowing where the NPP is…</p>
<p>Here is one of the useful details that I have uncovered from my work on stack effect (SE). To estimate the total SE available in a home at a given delta "t" simply multiply that temperature difference by the height of the house and by 0.007.</p>
<p>SE (pa) = .007 x ▲t (F) x ▲h (ft)</p>
<p>This gives you the total SE which gets divided in some proportion between high and low with that ever elusive neutral pressure plane (NPP) somewhere in between. </p>
<p>Now, knowing where the NPP is located can give you a hint as to how the leakage is divided between high and low. To get a rough position on it, substitute 1 ft for the height of the house and you get the SE pressure per foot inside the house. Take your baseline number at the front door (or anywhere) and divide it by that pressure per foot you just calculated and your NPP is that many feet above or below the height of your manometer.</p>
<p>If your resulting NPP is up near the ceiling, then you have more high leakage than low. If it closer to the floor, then you have more low leakage than high. Since you already know the inside and outside temperatures and you are going to take a baseline reading anyway, one simple calculation will provide you with one more piece of information that at times can be very useful.</p>
<p>Bud</p> Thanks for your reply, Bud.…tag:homeenergypros.lbl.gov,2013-10-12:6069565:Comment:1392402013-10-12T01:28:10.818ZSteve Waclohttp://homeenergypros.lbl.gov/profile/SteveWaclo
Thanks for your reply, Bud.<br />
<br />
"While you enjoy Kauai, remember, it was the cold air that started it all."<br />
<br />
I'll be sure to educate any locals who try to persuade me otherwise :-).<br />
<br />
Best wishes
Thanks for your reply, Bud.<br />
<br />
"While you enjoy Kauai, remember, it was the cold air that started it all."<br />
<br />
I'll be sure to educate any locals who try to persuade me otherwise :-).<br />
<br />
Best wishes Hi Steve, I'm retired as well…tag:homeenergypros.lbl.gov,2013-10-11:6069565:Comment:1394092013-10-11T23:30:10.471ZBud Pollhttp://homeenergypros.lbl.gov/profile/EverettPoll
<p>Hi Steve, I'm retired as well and thought I would get into energy auditing to keep busy. 20/20 hind sight tells me I should have taken up plumbing, but it has been fun.</p>
<p>Your example is a typical one where we have grown accustom to describing warm air moving up as rising and for the most part it does no harm. If only they had started 50 years ago telling people why. Without the why people have been left to their own imaginations and "hot air" has been credited with all kinds of…</p>
<p>Hi Steve, I'm retired as well and thought I would get into energy auditing to keep busy. 20/20 hind sight tells me I should have taken up plumbing, but it has been fun.</p>
<p>Your example is a typical one where we have grown accustom to describing warm air moving up as rising and for the most part it does no harm. If only they had started 50 years ago telling people why. Without the why people have been left to their own imaginations and "hot air" has been credited with all kinds of powers, from lifting balloons to the smoke that exits our chimneys.</p>
<p>While you enjoy Kauai, remember, it was the cold air that started it all.</p>
<p>Have a great vacation,</p>
<p>OH, and mechanical fans can do both, push and pull.</p>
<p>Bud. </p> Hello all
Doing some researc…tag:homeenergypros.lbl.gov,2013-10-11:6069565:Comment:1389972013-10-11T22:07:31.836ZSteve Waclohttp://homeenergypros.lbl.gov/profile/SteveWaclo
Hello all<br />
<br />
Doing some research for our trip to Kauai next week when these two paragraphs rang a bell. Always the provocateur, and not wanting to miss an opportunity to announce my vacation plans (hey, I'm retired and the wife and I earned this over many years of hard work :-), thought I'd toss this into the conversation:<br />
<br />
Kauai Trade Winds<br />
<br />
In Kauai, the northeast trade winds, averaging 12 mph, occur about 90% of the time in the summer and about 50% of the time in the winter. They keep humidity…
Hello all<br />
<br />
Doing some research for our trip to Kauai next week when these two paragraphs rang a bell. Always the provocateur, and not wanting to miss an opportunity to announce my vacation plans (hey, I'm retired and the wife and I earned this over many years of hard work :-), thought I'd toss this into the conversation:<br />
<br />
Kauai Trade Winds<br />
<br />
In Kauai, the northeast trade winds, averaging 12 mph, occur about 90% of the time in the summer and about 50% of the time in the winter. They keep humidity at a minimum and ensure moderate temperatures, especially on the windward, unlike other tropical islands closer to the equator. These cooling winds are created because warm air rises near the equator, flows northward through the upper atmosphere, and cools. Because it becomes heavier as it cools, it falls back to the earth’s surface at about 30 degrees latitude, where it flows back toward the equator to replace more rising warm air. This creates cool breezes moving from the northeast to the southwest along the ocean’s surface, and over the Hawaiian Islands.<br />
<br />
Now, if someone could tell me if my HVAC fan pushes or pulls air through my home, I'd be very appreciative :-)<br />
<br />
Best wishes. Hi Tom,
If there is one thing…tag:homeenergypros.lbl.gov,2013-10-10:6069565:Comment:1392002013-10-10T18:17:01.739ZBud Pollhttp://homeenergypros.lbl.gov/profile/EverettPoll
<p>Hi Tom,</p>
<p>If there is one thing I have learned from the physics forum it is that they can add confusion to any topic. I did read some of the thread you linked and surprisingly some of them managed to get it right.</p>
<p>1. Hot air does not "rise". It is pushed up by denser (cooler and/or drier) air underneath it. Stop the pushing and the air stops rising. Nothing moves against the pull of the force of gravity unless pushed by a stronger force.…</p>
<p></p>
<p>Hi Tom,</p>
<p>If there is one thing I have learned from the physics forum it is that they can add confusion to any topic. I did read some of the thread you linked and surprisingly some of them managed to get it right.</p>
<p>1. Hot air does not "rise". It is pushed up by denser (cooler and/or drier) air underneath it. Stop the pushing and the air stops rising. Nothing moves against the pull of the force of gravity unless pushed by a stronger force.</p>
<p><a href="http://www.physicsforums.com/showthread.php?t=32331&amp;page=4" target="_blank">http://www.physicsforums.com/showthread.php?t=32331&amp;page=4</a></p>
<p>Now, if anyone brings some of their "thermodynamics" questions back here I will need your help answering them. :)</p>
<p>Bud</p> B: http://www.physicsforums.c…tag:homeenergypros.lbl.gov,2013-10-10:6069565:Comment:1392052013-10-10T16:36:48.826ZTom DelContehttp://homeenergypros.lbl.gov/profile/tomdelconte
<p>B: <a href="http://www.physicsforums.com/showthread.php?t=32331">http://www.physicsforums.com/showthread.php?t=32331</a> unless you've taken thermodynamics(engineering, physics, chemical physics) five times, and taught it once, there's no way to understand it! That's why the old wives tales never die! enjoy, t</p>
<p>B: <a href="http://www.physicsforums.com/showthread.php?t=32331">http://www.physicsforums.com/showthread.php?t=32331</a> unless you've taken thermodynamics(engineering, physics, chemical physics) five times, and taught it once, there's no way to understand it! That's why the old wives tales never die! enjoy, t</p> Going back to the 4 responses…tag:homeenergypros.lbl.gov,2013-10-10:6069565:Comment:1392032013-10-10T15:25:41.880ZBud Pollhttp://homeenergypros.lbl.gov/profile/EverettPoll
<p>Going back to the 4 responses:</p>
<p>The first part of #1 is correct for a cooling climate, but the second part needs more discussion.</p>
<p>"The gable vent can supply a "short circuit" in that it will cool unevenly. There is still plenty of hot air rising here."</p>
<p>Since the air flow entering the soffits will actually be increased by leaving the gable vents in place, the neutral plane moves up, what portion of the attic will "cool unevenly"? And yes, there will still be plenty of…</p>
<p>Going back to the 4 responses:</p>
<p>The first part of #1 is correct for a cooling climate, but the second part needs more discussion.</p>
<p>"The gable vent can supply a "short circuit" in that it will cool unevenly. There is still plenty of hot air rising here."</p>
<p>Since the air flow entering the soffits will actually be increased by leaving the gable vents in place, the neutral plane moves up, what portion of the attic will "cool unevenly"? And yes, there will still be plenty of hot air being pushed out both gable and ridge vents.</p>
<p>#2. Done</p>
<p>#3. " If there is no backdrafting when the customer opens the window until things heat up, the problem is solved."</p>
<p>Actually, the problem has just been temporarily avoided. The more dangerous phase of the fire cycle comes as the fire is dying out and the home owner shuts the window and heads off to bed. With an outside chimney and a cold night, the draft can reverse before the last coals buried in the ashes die out. The switch from draft to backdraft can also be hastened by one or more exhaust appliances which will fill the chimney with cold air allowing it to remain in the backdraft mode after the appliance cycles off. Relying on homeowners to do things right fails to consider, it may not always be the home owner controlling the fire.</p>
<p>#4. This has been covered, but to restate, the warm air is being pushed up and out. It is an unwilling participant in this process as it is always being pulled down by gravity.</p>
<p>Bud</p> Bud
What you are saying makes…tag:homeenergypros.lbl.gov,2013-10-09:6069565:Comment:1390652013-10-09T15:24:23.655ZEd Minchhttp://homeenergypros.lbl.gov/profile/EdMinch773
<p>Bud</p>
<p>What you are saying makes sense:</p>
<p>"The cold air ends up at the bottom because it is heavier. The hot air moves to the top because the cold air displaces it."</p>
<p>However, if there were no warm air to get out of the way, the cold air would have nothing to react with. It's a totally symbiotic relationship. </p>
<p>Bud</p>
<p>What you are saying makes sense:</p>
<p>"The cold air ends up at the bottom because it is heavier. The hot air moves to the top because the cold air displaces it."</p>
<p>However, if there were no warm air to get out of the way, the cold air would have nothing to react with. It's a totally symbiotic relationship. </p> Ed, Michael, to be clear, I c…tag:homeenergypros.lbl.gov,2013-10-09:6069565:Comment:1390632013-10-09T14:07:55.867ZBud Pollhttp://homeenergypros.lbl.gov/profile/EverettPoll
<p>Ed, Michael, to be clear, I certainly agree that hot air goes up while cold air goes down. My objective is to clarify that hot air does not go up under its own power and it is my belief that the long established "hot air rises" phrase has inadvertently led to many wrong conclusion by far too many people.</p>
<p>All air, hot and cold, is subject to gravity and thus being pulled down. The cold air ends up at the bottom because it is heavier. The hot air moves to the top because the cold air…</p>
<p>Ed, Michael, to be clear, I certainly agree that hot air goes up while cold air goes down. My objective is to clarify that hot air does not go up under its own power and it is my belief that the long established "hot air rises" phrase has inadvertently led to many wrong conclusion by far too many people.</p>
<p>All air, hot and cold, is subject to gravity and thus being pulled down. The cold air ends up at the bottom because it is heavier. The hot air moves to the top because the cold air displaces it.</p>
<p>The confusion surfaces when people assume that the hot air moving up is responsible for that negative pressure below it that contributes to the corresponding infiltration. The reality is that negative pressure below is a result of the lower atmospheric pressure inside the house when compared to the outside. The actual negative number (wrto) will vary with temperatures and as the infiltration and exfiltration seek a balance by adding to or subtracting from the pressure within the house.</p>
<p>It is the heavier cold air from outside pushing in through the lower leaks that pressurizes the house to force the lighter hot air up and out.</p>
<p>Again, when cold air moves down there will be a corresponding flow of warm air moving up, but the only force exerted by that hot air is down.</p>
<p>Bud</p>